Partial coherence and optical vortices

by Maleev, Ivan.

Abstract (Summary)

Optical vortices are singularities in phase fronts of optical beams. They are characterized
by a dark core in the center and by a helical wave front. Owing to azimuthal components
of wave vectors, an optical vortex carries orbital angular momentum. Previously, optical
vortices were studied only in coherent beams with a well-defined phase. The object of
this dissertation is to explore vortices in partially coherent systems where statistics are
required to quantify the phase. We consider parametric scattering of a vortex beam and a
vortex placed on partially coherent beam. Optical coherence theory provides the
mathematical apparatus in the form of the mutual coherence function describing the
correlation properties of two points in a beam. Experimentally, the wave-front folding
interferometer allows analysis of the cross-correlation function, which may be used to
study partial coherence effects even when traditional interferometric techniques fail. We
developed the theory of composite optical vortices, which can occur when two coherent
beams are superimposed. We then reported the first experimental observation of vortices
in a cross-correlation function (which we call spatial correlation vortices). We found
numerically and experimentally how the varying transverse coherence length and position
of a vortex in a beam may affect the position and existence of spatial correlation vortices.
The results presented in this thesis offer a better understanding of the concept of phase in
partially coherent light. The spatial correlation vortex presents a new tool to manipulate
coherence properties of an optical beam.
To Inga